scientists say that the universe is expanding at an accelarated rate, and that is due to what they call dark energy.... So when supposed the expasion from the big bang get lower it' the opposite instead....

Then there is dark matter, that the scientists say is the force that avoids the stars at the far end of a galaxy to drift away from it in to deep space.

So it can be concluded that dark energy has a inverse effect of the dark matter. One tries to move it apart in to infinite, (but mass of the universe must be finite) and in the other side dark matter tries to glue it all together.

Dark energy and dark matter are what scientists have to add to their equations to get their cosmic numbers to work. Some evidence of their existence has been detected at least until a better explanation presents itself.
____________
Bob DeWoody

My motto: Never do today what you can put off until tomorrow as it may not be required. This no longer applies in light of current events.

Dark Energy:
Imagine the burning star, supernova explosion, matter fall into black hole, gamma ray burst, merging of two neutron stars, merging of two black holes..etc...all these events emit huge amount of energy in the form of radiation. Due to the vastness of space most emitted radiation(energy) will simply traveling in space for a long period of time before reaching the destinations.
Energy in the state of 'traveling' is call Dark Energy (source: imagination from myself)

Dark matter:
No one knows the total mass of all black holes in a Galaxy (example: Milky Way galaxy)
All the Dark Matter are actually reside at the singularity of black holes. (source: imagination from myself)

Actually the energy you speak of has already been accounted for as part of the "normal" universe. Also the matter contained in black holes has been allowed for. Dark energy and dark matter are not those things. They are beyond our normal means of measurement and hence the terms
____________
Bob DeWoody

My motto: Never do today what you can put off until tomorrow as it may not be required. This no longer applies in light of current events.